"She told me she just doesn't enjoy sex and getting pregnant was like work. I couldn't help but tell her she must be doing something wrong!"
WOW! I wouldn't dare talk like that to my friends! tell a friend that they must be doing something wrong?!
Sometimes it's the marriage in trouble, sometimes the guy is a slob, or maybe he's abusive and she's turned off that way, maybe he's ahhh, not toooo skilled shall we say? It doesn't have to be her fault. Sometimes it's a case of a disease undiagnosed and maybe she isn't aware she's ill.
Mothering, housework, jobs, pets, neighbors, also all take their toll on a woman's libio.
Personally, I never was too tired, too sick, or anything to enjoy a romp